Co-existence of blaOXA-23 and blaNDM-1 genes of Acinetobacter baumannii isolated from Nepal: antimicrobial resistance and clinical significance

Background: Molecular analysis of carbapenem-resistant genes in Acinetobacter baumannii, an emerging pathogen, is less commonly reported from Nepal. In this study we determined the antibiotic susceptibility profile and genetic mechanism of carbapenem resistance in clinical isolates of A. baumannii. Methods: A. baumannii were isolated from various clinical specimens and identified based on Gram staining, biochemical tests, and PCR amplification of organism specific 16S rRNA and bla(OXA-51) genes. The antibiotic susceptibility testing was performed using disc diffusion and E-test method. Multiplex PCR assays were used to detect the following beta-lactamase genes: four class D carbapenem hydrolyzing oxacillinases (bla(OXA-51), bla(OXA-23,) bla(OXA-24) and bla(OXA-58)). Uniplex PCRs were used to detect three class B metallo-beta-lactamases genes (bla(IMP), bla(VIM) and bla(NDM-1)), class C cephalosporin resistance genes (bla(ADC)), aminoglycoside resistance gene (aphA6), and ISAba1 of all isolates. Insertion sequence ISAba125 among NDM-1 positive strains was detected. Clonal relatedness of all isolates were analyzed using repetitive sequence-based PCR (rep-PCR). Results: Of total 44 analyzed isolates, 97.7% (n = 43) were carbapenem-resistant A. baumannii (CR-AB) and 97.7% (n = 43) were multidrug resistant A. baumannii (MDR-AB). One isolate was detected to be extremely drug resistant A. baumannii (XDR-AB). All the isolates were fully susceptible to colistin (MICs < 2 mu g/ml). The bla(OXA-23) gene was detected in all isolates, while blaNDM-1 was detected in 6 isolates (13.6%). Insertion sequence, ISAba1 was detected in all of bla(OXA-23) positive isolates. ISAba125 was detected in all bla(NDM-1) positive strains. The bla(ADC) and aphA6 genes were detected in 90.1 and 40. 1%, respectively. The rep-PCR of all isolates represented 7 different genotypes. Conclusion: We found high prevalence of CR-AB and MDR-AB with bla(OXA-23) gene in a tertiary care hospital in Nepal. Systemic network surveillance should be established for monitoring and controlling the spread of these resistant strains.